Sen. Dick Durbin's run for re-election against Republican Jim Oberweis promises to be a costly, rough-and-tumble contest in which the longtime Democratic lawmaker has key advantages.

In a closer-than-expected GOP primary race Tuesday, Oberweis emerged the victor, capturing 56 percent of the vote to Doug Truax's 44 percent, with 98 percent of the state's precincts reporting, according to unofficial returns.

Truax called Oberweis to concede, and later the victor declared that “it's safe to say” he had captured the nomination.

“I believe that if I win this Senate seat, it means that the Republicans will be taking control of the U.S. Senate and that will change the direction of this country,” Oberweis told supporters.

Durbin, who ran unopposed on the Democratic side, thanked supporters in an email Tuesday and asked for campaign cash. “Now that self-funding, ultra-conservative Jim Oberweis has been nominated, I'm going to need you even more,” he said.

Durbin, 69, is seeking his fourth term in the U.S. Senate in a campaign that some believe will be his last hurrah.

Oberweis, 67, a multimillionaire dairy owner and investment manager, will be running uphill in a Democratic-leaning state. Though he won a state Senate seat in 2012, he racked up five defeats for major office beforehand and has the battle scars to prove it.

This year's primary left him with new wounds. Truax, 43, from Downers Grove, slammed him as a “snowbird” for vacationing in Florida in the week before the election just as a snowstorm barreled down on Chicago. During his victory party at an Oberweis ice cream parlor and hamburger restaurant in Glen Ellyn, Oberweis told reporters the Florida trip was not a good political decision.

In the general election, Durbin, the incumbent, has inherent advantages: a sizable staff to advance his interests and help Illinoisans, a record of luring federal dollars to Illinois, and, as a native of East St. Louis, support in the more conservative Democratic enclaves downstate and in heavily Democratic Cook County.

He's a top ally to President Barack Obama, who remains more popular in Illinois than across the nation.

Oberweis, from Sugar Grove, followed a strategy of ignoring primary opponent Truax, a business owner, West Point graduate and former Army Ranger. Citing the press of legislative business, Oberweis agreed to only one debate. With a strong lead in polls, deep pockets and high name recognition, Oberweis could afford to snub Truax. Thus it was tough for Truax to raise cash and persuade more GOP voters to give him a serious look.

A first-time candidate, Truax ran more strongly than some had predicted, considering that he trailed Oberweis 52 percent to 18 percent in a Tribune/WGN-TV poll taken March 1-5.

He said he would “absolutely” support Oberweis 100 percent. “I think that Dick Durbin has to go,” Truax told the Tribune.

He would not commit to a future run for office. He said supporters had told him, “Don't go away,” and up next for him is a Republican unity lunch Wednesday in the Loop. Oberweis, however, will not attend the lunch “because of his commitments in Springfield,” an Oberweis spokesman said.

After the lunch, Truax said, he plans a “spring break.”

Now Oberweis is what Truax was: an underdog. And the GOP nominee stands to get the cold shoulder from Durbin.

“Durbin is going to ignore Oberweis as long as he can — until his polls show that Oberweis is emerging as a serious threat,” said Wayne Steger, chairman of political science at DePaul University.

Steger said Oberweis risks “being haunted” by past campaign gaffes. He also said Oberweis lacks some of the attributes of the Republican who holds Illinois' other Senate seat, Mark Kirk, a political moderate with statewide appeal.

“The Republican Party of Illinois has conceded this election to Durbin,” said Mezey, who noted that incumbents are thrown out when taken on by “quality challengers” with campaign cash and political experience, which afford them higher name recognition.

“Oberweis has the money, but he is not a seasoned politician,” Mezey said.

Campaigns are about contrasts, and the candidates' differences will be made clear in a fusillade of attacks and counter-attacks.

Durbin, the Senate's No. 2 Democrat, is likely to cast Oberweis as too right-of-center and as a serial loser whose wealth (and $1.3 million Florida penthouse) makes him out of touch with ordinary Illinoisans. Oberweis' pre-primary Florida trip could help Durbin make the case that Oberweis is not engaged.

By contrast, Durbin, who is the assistant Senate majority leader, was in Ukraine last week to try to help resolve its political crisis. He returned Sunday and talked about the situation in Crimea on NBC's “Meet the Press.”

Oberweis, who made a fortune from his investment firms along with his milk and ice cream empire, no doubt will continue to sound an anti-incumbent, anti-Washington message and tag Durbin as too liberal.

The Republican nominee issued a statement late Tuesday that highlighted his 40 years in private enterprise and Durbin's 30-plus years “on the government payroll.”

Oberweis has emphasized that Durbin was pivotal to passage of Obamacare, whose launch has been troubled.

“Obamacare is increasingly unpopular and Oberweis will come after him,” in keeping with to the GOP national strategy to capture seats in Congress, Steger said. “He'll point out the flaws and problems of Obamacare,” a vulnerability that Durbin must confront.

Oberweis has argued that the state's senior senator has been in Washington too long and that under his watch, the federal deficit has soared and the economy sputtered. Durbin entered the U.S. House in 1983 and the Senate in 1997.

Oberweis has his own potential headaches on public policy. “His ideologically extreme statements are going to come back and haunt him in attack ads,” Steger said.

In his 2004 race for the U.S. Senate, Oberweis' TV ads showed him in a helicopter over Soldier Field, asserting that enough “illegal aliens” cross the border and steal jobs to fill the stadium every week. The ad provoked a strong backlash.

Transparency could emerge as an issue. Durbin has made public his tax returns, including them in the annual financial disclosure required of federal lawmakers. Oberweis and Truax were asked by the Tribune to release their returns, but refused.

In campaign cash, Durbin reported nearly $5.7 million in his war chest as of Feb. 26. Oberweis, after lending his bid a half-million, had $547,000 then. He has poured in millions of his own money into past races, and he may do so again to achieve closer parity with Durbin.

The dynamics of Illinois and national politics put Oberweis at a disadvantage.

Matt Streb, chairman of political science at Northern Illinois University, said Illinois Republicans will focus on sending one-term Democratic Gov. Pat Quinn packing and the national party will zero in on competitive Senate races in states such as Arkansas, Kentucky, Louisiana, Michigan, Montana, North Carolina and West Virginia. The GOP wants to regain control of the Senate, so it will take the fight to places where its chances are better.

“Nothing that I've seen or read,” Streb said, “indicates that Durbin is in any sort of trouble.”

Durbin is not taking any chances, amid concerns about apathy among Democrats in a nonpresidential election year.

He's launching a statewide tour that runs through Sunday and ratcheting up voter registration among traditional Democratic allies, including young voters and minorities, said Ron Holmes, his campaign spokesman.

One key theme: Obama needs allies such as Durbin to carry forward his initiatives during the next two years, Holmes said.

Inadequate training, technological glitches, locked doors and missing poll workers led to dozens of voting delays at Chicago polling places Tuesday, officials said, even as city and county voter turnout appeared to reach historic lows.

Illinois primary election day dawned Tuesday with voters getting to shape the Republican and Democratic fall tickets for contests ranging from governor and U.S. Senate down to the state legislature and county board.